Factors influencing surface carbon contamination in ambient-pressure x-ray photoelectron spectroscopy experiments

Abstract

Carbon contamination is a notorious issue that has an enormous influence on surface science experiments, especially in near-atmospheric conditions. While it is often mentioned in publications when affecting an experiment’s results, it is more rarely analyzed in detail. We performed ambient-pressure x-ray photoelectron spectroscopy experiments toward examining the build-up of adventitious carbon species (both inorganic and hydrocarbons) on a clean and well-prepared surface using large-scale (50 × 10 mm2) rutile TiO2(110) single crystals exposed to water vapor and liquid water. Our results highlight how various factors and environmental conditions, such as beam illumination, residual gas pressure and composition, and interaction with liquid water, could play roles in the build-up of carbon on the surface. It became evident that beam-induced effects locally increase the amount of carbon in the irradiated area. Starting conditions that are independent of light irradiation determine the initial overall contamination level. Surprisingly, the rate of beam-induced carbon build-up does not vary significantly for different starting experimental conditions. The introduction of molecular oxygen in the order of 10 mbar allows for fast surface cleaning during x-ray illumination. The surface carbon contamination can be completely removed when the oxygen partial pressure is comparable to the partial pressure of water vapor in the millibar pressure range, as was tested by exposing the TiO2(110) surface to 15 mbar of water vapor and 15 mbar of molecular O2 simultaneously. Furthermore, our data support the hypothesis that the progressive removal of carbon species from the chamber walls by competitive adsorption of water molecules takes place following repeated exposure to water vapor. We believe that our findings will be useful for future studies of liquid-solid interfaces using tender x rays, where carbon contamination plays a significant role.

Probing dynamic covalent chemistry in a 2D boroxine framework by in situ near-ambient pressure X-ray photoelectron spectroscopy

“…This is confirmed also by the spectra acquired after evacuation of the cell ( p H 2 O < 1 × 10 −6 mbar). Here, the residual oxygen signal is attributed to surface contamination due to the water-induced displacement of oxygen-containing carbonaceous species from the internal chamber walls, 48,49 as suggested also by the C 1s spectra shown in Fig. SI3 †.…”

Conformational heterogeneity of molecules physisorbed on a gold surface at room temperature

“…As a sample system, BCB molecules were spin-coated on a thin metal film and covered by an Al 2 O 3 capping layer to suppress rotational and spectral diffusion 5 . The capping layer not only provides a freeze-frame for individual molecules, but also protects them from unwanted chemical contamination under ambient conditions, especially by sulfur 43 and carbon 44 molecules. Moreover, it prevents possible contamination of the Au tip, e.g., adsorption of the probing molecules onto the tip surface that can cause artifact signals, as shown in Fig.…”

ALD-fabricated two-dimensional SnO2-In2O3 n-n nanohybrid electrode for electrochemical supercapacitors

“…3a shows the XPS survey spectra of electrode, which represent the presence of characteristics elemental peaks of Sn 3d, Sn 4d, In 3d, In 4d, In 4p, and O 1s in their reported binding energies [36,39]. Additionally, a C 1s peak is observed in the sample that is possibly arising from the ubiquitous carbon contamination [39,40]. The deconvoluted and fitted core-level XPS spectrum of Sn 3d, In 3d, and O 1s spectra are presented in Fig.…”